1. Field of the Invention
The present invention relates to a matrix type display panel, and more particularly to an active matrix type liquid crystal display panel formed with matrix electrode plates in which a driving switching element array is integrally provided.
2. Description of the Prior Art
Typical advantages given by liquid crystal display panels are as follows:
(1) Being passive display devices, requiring small power consumption.
(2) Low voltage operation is possible.
(3) Display devices of panel structure are easily constituted.
(4) Large-sized display is possible.
Luminescent (active) display devices cannot provide these advantages.
Among such liquid crystal display panels, an attention is paid particularly to a liquid crystal display panel employing a matrix-driving scheme for a plurality of picture elements as disclosed in U.S. Pat. No. 3824003 (Japanese Laid-open Patent Application No. 17599/1975).
The liquid crystal display panel of this type has a structure, for instance, as shown in FIG. 1(a).
An electrode plate (of glass, plastic film, etc.) constituting a display panel is formed by arranging thin film transistors (each of which will be called "TFT" hereinafter) for driving in the form of a matrix with a density of about 2 to 10 lines/mm.
TFTs have several types of structure. In this embodiment, by way of example, so called "stagger structure" in which gate electrodes as shown in FIG. 1(a) are formed on an electrode plate will be described.
The TFT comprises gate lines 1aa, 1ab, . . . (row electrodes) formed on an electrode plate S, gate electrodes 1a, 1b, 1c, 1d . . . provided on the gate lines, insulating layers one of which is designated by 5a stacked on gate electrodes, thin film semiconductor layers 2a, 2b, 2c, 2d, . . . formed on gate electrodes through the insulating layers, source lines 3a, 3b, . . . (column electrodes) provided close to one end of each semiconductor, drain electrodes 4a, 4b, 4c, 4d, . . . (electrodes constituting display units) provided close the other end of each semiconductor, etc. The row electrodes an column electrodes are formed of transparent or non-transparent (e.g., metallic) film conductive layers.
FIG. 1(b) is a plan view which is viewed in the direction of an arrow OB of FIG. 1(a), partially showing a matrix driving circuit.
FIG. 2 shows a cross sectional view of the display panel formed with electrode plates having cross sectional structure taken along the line A--A of FIG. 1(b).
In FIG. 2, reference numerals 7 and S designate electrode plates of glass, plastic film, etc., reference numerals 4c and 4d designate the above-mentioned drain electrodes, and reference numeral 8 designates a counter electrode.
The drain electrodes 4c and 4d, and the counter electrode 8, etc. are formed of a transparent conductive film of Sn0.sub.2, In.sub.2 0.sub.3, ITO, etc., or a metallic film of Au, Al, Pd, etc.
As previously mentioned, reference numerals 1c and 1d, and 3a and 3b designate gate electrodes and source electrodes, respectively, both of which are formed of a metallic film of Al, Au, Ag, Pd, etc.
Reference numerals 5a, 5b and 9 designate insulating layers. Reference numerals 2c and 2d designate thin film semiconductors of amorphous silicon, polysilicon, CdS, CdSe, etc. Reference numeral 10 designates a seal member. Reference numeral 11 designates a liquid crystal layer.
In the liquid crystal display panel thus formed, there is employed a display mode, e.g. the dynamic scattering mode (DSM), the twisted nematic (TM) mode, etc.
When a display device formed with a liquid crystal display panel is designed as a transmissive type or reflective type device, optical detecting means such as a polarizing plate, a .lambda./4 plate, reflective plate, etc., may optionally be required. Particularly, when the TM mode is employed as a display mode of the display panel, a polarizer 22 and an analizer 23 are used as optical detecting means.
With display panels thus formed, operating characteristics of the liquid crystal cell highly depend upon the thickness of the liquid crystal layer and overall display characteristics of the display panel are apt to be degraded. For this reason, in order to obtain preferable gradation and high-speed response characteristic, it is required that the thickness of the liquid crystal layer is as thin and uniform as possible (for instance, a few .mu.m to 10 .mu.m) over a certain area or wider (for instance, more than 10 cm.sup.2).
From this point of view, in order to keep constant the thickness of liquid crystal layer, there is well known a method of mixing inactive members each having a predetermined particle diameter into the liquid crystal layer. However, with this method, it is difficult to mix the inactive members uniformly over an overall broad display surface, and the orientation of liquid crystal molecules can be disturbed at some portions at image display units or elements. Accordingly, this method cannot practically be used.